Multiple balancing  arrangement for multiplex transmission



June 12, 1923;

1 v L. ESPENSCHIED MULTIPLE BALANCING ARRANGEMENT FOR MULTIPLEX TRANSMISSION 1 Filed Aug, .29, 1919 v 5 Sheets-Sheet l I N VEN TOR.

ATTORNEY Jim 12, 1923. I I 1,458,225 L. ESPENSCHIED V MULTIPLE BALANCING ARRANIEEMENT FOR MULTIPLEX TRANSMISSION Filed Aug 29, 1919 5 Sheets-Sheet 2 IN V EN TORL 7+) F2 4 AZI WM June 12, 1923. 1,458,225. L. ESPENSCHIED MULTIPLE BALANCING ARRANGEMENT FOR MULTIPLEX TRANSMISSION Q Filed Aug. 29 1919 5 sh eets sheet 5 IN VEN 710R.

LZ vazsam ATTORNEY June 12, 1923. 7 1,458,225 L ESPENSCHIED MULTIPLE BALANCING ARRANGEMENT FOR MULTIPLEX TRANSMISSION Filed Aug 29. 1919 5 She -wt 5 r I 6 K &mrykr 35 i'c i'cizV seao i E HEW/fer 590ml H g I r fiflgarlz'e r INVENTOR. 420A H .ilspewcm' BY ATTORNEY Patented June 12, i923.

nnirsn stares PATENT crrics.

LLOYD ESPENSCI-IIED, 0F HOLLIS, YORK, ASSIGNOR 1C0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEXV YORK.

MULTIPLE lBALi-ilfi'SING ARRANGEMIENT FDR MULTIPLE TRANSMISSION.

Application filed August 29, 1919. Serial No. 320,661.

and more particularly to multiplex systems in which high frequency I carrier currents are used for the transmission of signals.

One of the objects of this invention has reference to the provision of a multiplex system in which the common transmission line over which a plurality of signals may be simultaneously transmitted is balanced by a single artiiicial line or balancing network. Another object of the invention has reference to the provision of a multiplex system in which each transmitter is so associated with the common transmission line that energy therefrom impressed upon the transmission line will be not only substan tially without effect upon the receiver at the same station, but will also be substantially without effect upon the receivers associated with other channels Other and further objects of the invention will more fully appear hereinafter as the description of the invention proceeds.

The objects of this invention may be attained by providing multiple connections between the common transmission circuit and its balancing artificial line or network and separately associating a receiving and.

a transmitting element for each channel with each multiplex connection in such a manner that one of the two elements will be inductively connected to the corresponding multiple connections, while the other of said elements will be connected to neutral points of said multiple connectionwith respect to the first element. It will be understood, of course. that the arrangements of this invention may be applied to any form of inulti pleX system and are equally applicable to multiplex transmission over wire transmission lines or to multiplex transmission in connection with radio telephony and telegraphy. I v

The mventionmay now be more fully understood by reference to thefollowing description, when read in connection with the accompanying drawings, Figures 1 to 8 inelusive, of which are simplified diagrams of a number of embodiments of the invention while Figs. 1 to at, inclusive, illustrate how the antenna may be replaced by a wire transmission line in circuits embodying the present invention.

lrleferring to Fig. 1, A designates an antenna, such as is used in radio telephony or telegraphy and N designates an artificial line or network adapted to balance the antenna or other form of transmission circuit over which a plurality of signals may be simultaneously transmitted. v The antenna is associated with the artificial line or network N through a plurality ofmultiple connecthrough a selective means herein illustrated as a tuned circuit and through a transformer arrangement 11 having windings in each of the sections 1 and 1 of the multiple connection. The transmitting device or element conventionally indicated at T is bridged between the sections 1 and l of the multiple connection at the mid points of the windings of the transformer 11. so as to be neutral with respect to" the receiving device R It will be understood, of course, that the transmitting and receiving devices or elements T and R may be of any desired character and may include any of the well known arrangements for modulation, demodulation and filtering employed in connection with radio telephony or telegraphy or other forms of multiplex carrier systems.

Receiving devices or elements and T are similarly associated with the multiple connection 2+2, through the transformer -12, while the receiving devices or elements T and R are likewise associated with the multiple connection 33 through the transformer 13. It will be observed that the connections of the various transmitting and receiving devices are such that energy applied from any transmitter such as T to the coininon transmission circuit such as antenna it or the line L Will besubstantiaily without effect upon not only the corresponding receiver il but also the receivers and R associated with other multiple CODDCCtlOllS.

An alternative arrangement is illustrated in Fig. 2 in which the invention is shown as applied to a system en'naloying a ground return as distinguished lrom a hill in c system. Similar elements in the two inagrams are designated by the same reference characters. In 2 it will he noted, that each 01 the transmitters 'l l.. and 'l are connected to ground instead of metallic return conductors of the multiple connections. The balancing artificial line or network N is also connected directly to ground instead of being connected through metallic conductors of the multiplex connections to the return wires of the traiunnissii'm line or to the grounded section of the antenna. In case the antenna of Fig. 2 is replaced by is and need not be Fig. 3 shows an arrangement somewhat similar to Fig. l, but ennnloying ti. .ing rangements in the multiple o u-hes order to provide for the separation of several channels instead of providing frequency separation by locating; lilters in the local trzuismitting and receiving circuits. It will be noted that the multiple branches 1. 2 and 8 contain filters which are conventionally indicated. at F F and F These filters may he simple tuned cirsc-uits as in Fig. l, but where a (2:: tier x-nrrent is modulated by a low frequency sr nal volving a band of 'ti'QQI'lQDClGS ot' considerable width, it is preferable to use broad band filters oil the type illustrated in United States patents to George A. Campbell llos. 1227.113 and 1.22'?.l...l dated irla v 23 um. Balancing means FL" and i ore ineluded in the multiple balancing circuits l. 2' and 3' for the nrpose of balancing the filters F F and F The balancing n'ieans may be simply oroad band filters identical in construction with the filters F F and F or they may be networks of acter having electrical character lating those of the filters. ansmitting and receiving circuits T 1 et may be of any character and where the invention applied to a system -i1ploying carrier currents, these transmitting and receiving cir- The tr cuits will contain suitable modulating and demodulating apparatus as Well as filters and amplifiers when desired. The operation of the arrangement oi Fig. 3 is similar to that of Fig. l and need not be described.

Fig. t illustrates an arrangement similar to that of Fig. 3 but differing therefrom in that the .multiple branches are connected in series instead or? in parallel. In this figure, iple branches l, :2 and 3 including F F and F are connected in L--'.el'1';).'-; witi each other and with the circuit lea 'ing to the line L or the antenna A as tie case may be. Similarly the balancing multiple branches 1, 2 and 3, containing the filters F and 1 are connected in series with each other and with the artificial balancing network ll. The filters function as in 3. to separate the frequencies into the proper channels. The operation is in general similar to that oi Fig. 3, and will be obvious without further description.

Fig. 5 illustrates a manner in which the principles of the invention may be applied to a multiplex system employing carrier currents. In this figure ML designates the main transmission circuit, which may be either a wireless" antenna or an ordinary wire transmission line, while L L and L indicate low frequency signaling lines such as for instance, telephone lines, the signals from which are to be superposed uponthe main line ML. The main line ML is associated with the balancing artificial line or network MN through the bridge connections l1, 2-2, 3-3 etc, each of Which bridge connections includes pairs oi filters HF l l LE lll HF Hi l. etc. These filters may he oil the broad band type illustrated and described in the Campbell patents above referred to. and are so designed as to transmit a band or frequencies in the neighborhood of the basic carrier frequency assigned to each bridge connection, the band being o't sutlirient width to allow for the variation in frequency correspoiuling to the low frequency signaling currents.

The bridge connection l-1 is associated through a. transformer ll with transmitting channel 'lL and receiving channel 11L in which are included the necessary translating devices for translating the low frequenry signals into carrier currents and vice versa. The channels "lL and R-L are associated with the low trequei'icy signaling 1 of the transformer 11.

such for instance, as the well known vacuum tube modulator. As 'modulators of this character are commonly understood inthe art, the details of this apparatus are not,

illustrated, schematically.

and it is merely indicated the filters HF and HF The amplifier TA, may be of any well known character, but is preferably a vacuum tube amplifier of WQllkIlOWIl type, and as the details of such amplifiers are well known and constituteno part of the present invention, the amplifier is merely indicated schematically.

The receiving channel RL includes a detector D an amplifier RA, and a band filter R1 The detector D may be any well known detecting arrangement for translating carrier currents into low frequency signaling current, and is preferably a detector of the well known vacuum-tube type. As the detail of this structure forms no part of the present invention, the detector is indicated schematically. The amplifier RA, may be of any wellknown type, such, for instance, as the vacuum tube amplifier, and is likewise illustrated schematically, as the details of such amplifiers are well knownand constitute no part of the present inventioir The filter- RF, is a band-filter of the type illus trated in the Campbell patents hereinbefore disclosed, and is preferably so designed as to transmit a range of frequencies correspond} ing to the range of low frequency signaling currents employed in transmitting signals over the line L The lines L and L are associated with the bridge circuits 2-27 and 3 3 respectively by means of transmitting andreceiving car rier channels, including apparatus similar.

to that just described. The filters RF, and RF; of the receiving channelsRL and R12 respectively are'similar to the filter RF L The filter TF ofthe transmitting channel TL is similar to filters HF and H F while the filter TF of the transmitting channel TL, is similar to the filters HF andHF ML and the other half flowing through the filter HF, over the circuit 1 to the artificial line .MN. Owing to'the bridged relation of the circuits '1--l, 22' and 3-3, this trans' The filter TF is a broad band filter similar in structure to, and trans-' mitting a range of frequencies the same as,

spectively. The modulated mitted energy is balanced withrespect to all the receiving channels so that substantially nointerference is produced. By means of the fre uency separation due to the filters HF F etc., interference between both receiving and transmitting channels is further reduced. It will be understood, of course, that signals incoming from the line L, and L' will modulate the carrier frequencies assigned to the bridge circuits 2-2 and 3.-3 respectively, and may be impressed upon the line ML simultaneously with the currents: from the line L without producing interference.

Carrier currents modulated in accordance with signals at a distant station, and transmitted over the line ML are selected by means of the filters HF,, HF and into I the correspondingbridged circuits, and pass through the transformers'll, 12 and 13 .to the receiving channels RL RL and RL recarrier frequencies thus transmitted by the circuit RL, are detected by the detector D in a well known manner, the resulting low frequency signaling currents being then amplified by the amplifier RA, and transmitted through the band filter RF, to the line L Similaroperations may simultaneously 'take place with respect to the receiving channels RL, and RL i i Fig. 6 illustrates the manner in which the bridged arrangement of circuits .may be utilized for preventing interference between low frequency signaling currents and high frequency carrier currents where a carrier system is superposed upon an ordinary low frequency signaling line. I In this-fi 'ure,ML denotes a transmission line over which low frequency signal transmission and carrier transmission may simultaneously take place.

The main line ML is associated with a balancing artificial line or network MN through a low frequency bridge connection 100--l 00 and through a high frequency or carrier bridge connection 200-200. The low frequency bridge circuits 100-100 include low pass filters LF and LF respectively. These low pass filters are of the general type disclosed in the patents to Campbell above referred to, and are adapted to transmit a range of frequencies from zero up to the highest frequency utilized in connection with the transmission of low frequency signals from the terminal signaling line LT, which, as illustrated, is connected to. the junction point of the circuits 100-400. Line LT may be an ordinary terminaltelephone circuit including the usual composite apparatusetc. (not shown). The carrier bridge circuits 2004200 include high pass filters HF and HF respectively. These filters are of the type illustrated in the pat ents to Campbell above referred to, and are so designed as to transmit all frequencies same lines.

above alower limiting frequency which is so chosen as to be above the highest frequency transmitted over the terminal line A common carrier transmission circuit TL, and a common carrier receiving circuit llL, are associaten with the bridge circuits QOO200 through a balanced transformer arrangen'ient 20, the connections being); such that the circuits TL and RL are conjugate with respect to each other. T he circuit TL has associated therewith, transmitting channels TL Th etc, correspondineto signaling lines which may be similar to the lines L 'L etc. of Fig. 5. The circuit RL has associated therewith carrier receiving chan nels llL PL etc. corresponding to the The association of the carrier receiving and transmitting channels with the low frequency signaling lines may be through transformer arrangements similar to the transformers 11, 12, etc. of 1, but for simplicity these connections are not illustrated. Transmitting; channels TL, and TL include band filters Th, and Th so designed as to transmit a band of frequencies in the neighborhood of the carrier frequency assigned to each channel, the width of the band being sufficient to take care of the frequency variations corresponding to the low frequency signals. Similar band filters Pl? RF, are included in the receivingchannels lill EL etc.

The operation is as follows: The energy of low frequency signals incoming from the terminal lino LT divides between circuits 100 and 100, half flowing through the filter LP to the main line ML; the other half flowing through the i'ilter Ll to the balancing network MN. Owing to the bridged relation of the circuits 100 100 and 200-200 such portion of this energy as gets through filters HF and HF is substantially without effect upon the receiving circuit BL and consequently no interference with the receiving channels RL BL by low frequency signals from the terminal line l Low '1. results. frequency signaling currents incoming from the line Mli pass through the filter Ell to the line lfl, being substantially prevented from entering the carrier apparatus associated with circuit 301) by means of the high frequency filter HF.

Interference with the low ilrcqucncy signah ing currents of circuit ll'l by the higher frequency carrier currents of circuit TL be prevented by reversing the wires of bridge connection. 100 or 100 and for this purpose a switch is shown in the connection 100. Under this condition carrier currents from the transmitting channel TL, pass through the filter F, and are transmitter through the transformer 20 to the bridge circuit 200200. Owing to the bridged relation between the carrier apparatus and the apparatus associated with the terminal line LT, together with the filtering action of the filters L? and Li the carrier energy is substantially without effect upon said line LT, but passes through the filter HF to the main line ML. Carrier currents received over the line ML transmitted through the high pass filter HF into the circuit 200 and from this into the receiving circuit Ell where they are selected by means of the filters RF ll i etc. to the receiving channels Bill RL etc. Owing to the diii'erential connection between circuits BL and Tl], the received carrier currents do not -ct upon the transmitting channels TL, and Tl); etc.

Fig. 7 shows an arrangement in which each carrier channel associated with the main line .l'lL throup'h the balanced bridge gement. while the balanced bridge connection also employed for the low frequency terminal line LT. This arrangement dlfers from that of 6 merely in that the tran mitting and receiving channels oi each carrier circuit are rendered conjugate through the balanced bridge arrangement instead of securing conjugacy by means of the d fferential connection employed in 6. instead oi designing the network ll-llfil in Fig. '7 to balance the main line ML at all frequencies, this network may be merely dcsigned to balance said line at the low frequencies transmitted from the terminal line ill in which case separate networks little, and ldh may be employed for balamringtoe line ML with regard to the carrier frequencies assigned to the channels associated with the bridge connections 1l, 2 2 etc. The op ration of this circuit will be obvious from the operation described in connection rith previous circuits, and need not be further considered.

Fig. 8 illustrates an arrangement in which low i equency telephone currents, Morse signaling; currents, low frequency alternatmg 1 frequency carrier channels are supered upon a common transmission line, the Horse and low frequency alternating current systems being associated with the remaining circuits by a differential connection, while the telephone and high frequency carrier channels are connected in multiple bridged relation. As shown, the terminal telephone line LT is associated through a transformer 10 with a transmitting channel T and a r ceiving channel B which are rendered conugate with respect to each other by balancing the terminal line by means of a network NT. The channels T and R are associated with the bridge connection 100100 through a balanced transformer arrangement 10.

The several high frequency carrier channels are similarly associated with the bridge connections ll, 2-2, 33 by means of transformers ll, 12 and 13. Instead of intelegraph currents and a plurality of eluding, the filters for the high frequency channels in the bridge circuits, as in Figs. 5.

corresponding receiving channel;,thus the.

transmitting frequencies of. the transmitting; channels TL TL and TL m'ay be 2500 2800 and 3100 cycles respectively; while the corresponding receiving frequencies for the channels liL ,v RL and BL]. may be 3600, 3900 and @200 cycles respectively. I

The transmitting and receiving channels T and R of the terminal line LT are. provided with filters TF and adapted to transmit frequencies lying within the ordinary telephonic range while suppressing frequencies above andv below such range. If desired, amplifiers TA. and may be included in the circuits T and R as indicated schematically. These amplifiers may, of course, be of any well known type,-such as a vacuum tube amplifier. Branch circuits BM and BC are connected to themidpoints of the windings of the transformer 10 in the same manner as 1 the transmitting channel T of the telephone circuit, these branch circuits being; thus differentially connected to the remaining circuits in order to facilitatejsin perposition of a Morse telegraph system and a low frequency alternating current telegraph system upon thetransmission line ML. ii.

band filter FC is included in the circuitBG I for transmitting the frequencies assigned to the alternating current telegraph channel, anda band filter FM is inclined in the circuit BM for transmitting Morse frequencies. The Morse circuit may include a differential receiving relay having an armature whose contacts control the Morse receiving circuit RM. The Morse transmitting circuit TM is connected to the midpointsof the difierential relay DR. In ordertorender the transmitting and receivingv Morse channels conjugate, the filter FM is balanced by means of a filter FM, while a network NM is provided to balancethe circuits be-.

yond. the, filter FM.

The alternating current telegraph appara tus may comprise a transmitting circuit TC and a receiving circuit BC associated with the branch BC through a transformer These circuits may be rendered conjugate by balancing thefilter FC by means of an equivalent filter F0 and by providing a balancing network NC for balancing the'circuit beyond the filterFC- The operation of thehigh frequency carrier channels *1, 2 and 3 will be apparent from the. description of the operation of ternatine: tel

the amplifier TA. and are then passed.

'hrough-the filter Tl to the line ML. Low frequency telephone currents incoming from the line ML are transmitted through the transformer 10 and pass through the filter El to the receiving circuit R. After being amplined by the amplifier RA, such tele' phone currents are transmitted through the transformer L to the line LT. a Low frequency alternating currents the telegraph channel TC are transmitted from through the transformer TT and pass" through the filter FC transformed 10, the energy being then divided, one half of the higher frequency "in terference tendingcomponents being; transmitted to the line liiL and the other half to the balanci network MN. Since this current is applies to the mid points of the wind.-

ings of the transformer 10; no reaction is caused an the receiving channels such the telephc. e receiving; channel B or the car ier receiving channels 3L PUL etc. Al-

raph currents received from into thebran ch BCv to which the line ML 1 .d with the other channels substam the windin s of the differential relay DR without operating; said relay. and. are then transmitted through the filter FM over the branch EM and are then applied to the mid points of the windings of the transformer 10. so that they do not react in the receiving channels R, EL etc. Morse currents received from the line ML pass into the branch owing to the action of the filter FN, be ing suppressed from the other channels by meansof the filters therein. The received -Morse currents in the branch BM flow serially through the windings of the differential relay DR and actuate such relay to transmit the signals to-the Morse receiving circuit RMQ b I r While the'invention has been embodied in certain circuit arrangements which are considered desirable from a practical standpoint, it will be obvious that the general principles herein disclosed may be embodied in many organizations widely different from over the branch BC to the-mid points of the windings of the they are admitted by the filter EU, the filters eventing;- such currents from 'reactthose illustrated, without departing from the spiritot the invention as defined in the tollowin claims,

What is claimed is:

1. In a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality oi": receiving devices and a plurality oi? transmitting devices, selective means discrimin SlVQ between difler ent alternating current 'l'requencies for maintaining frequency separation between dirferent'sets oi transmitters and receivers, and separate means for simultaneously associatmg each of said receiving devices with said transmission circuit and said balancing means, said transmitting devices being so associated with saidtransmission circuit and said balancing means that energy from said transmitting devices will be applied to points neutral with r spect to said receiving devices.

2. In a multiplex signaling system, :1

transmission circuit. a balan means therefor, a plurality of receivin devices and a plurality of transmitting devices, selective means discriminative between different alternating current frequencies for maintaining frequency separation between different sets of transmitters and receivers, and separate means for simultaneously associating each of said receiving devices with said transmission circuit and said balancing means, said transmitting devices being so associated with said transmission circuit and said balancing means that energy from said transmitting devices will produce substan tially no effect upon the corresponding receivers. 3.111 a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means, a. plurality of transmitters and receivers, selective means discriminative between different alternating current frequencies for maintaining frequency separation between different sets of transmitters and receivers, circuit connections for simultaneously associating a transmitter and receiver with each of said parallel connections, said circuit connections being such that energy supplied from any one of said transmitters to said transmission circuit will be substantially Without efiect upon the corresponding r ceiver.

4.111 a multiplex signaling system, a

transmission. circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means, a plurality of transmitters and receivers, selective means discriminative between different alternating current-frequencies for maintaining frequency separation between different sets of transmitters and receivers, circuit connections for simultaneously associating a transmitter and receiver with each o'l said parallel connections, said circuit connections being such that energy supplied from any one of said transmitters to said transmission circuit will be substantially without effect upon any of said receivers.

5. ln multiple); signaling system, a transmission circuit, balancing means therefor, a plurality ot parallel connections be tween said circuit and balancing n cans, transmitting and receiving elements for each parallel connection, a transformer balanced to establish conjugate circuits associating one of said elements with the corresponding parallel connection, the other of said elements being so associated with said parallel connection that energy trom the transmitter will produce substantially no effect upon the receiver.

6. in a multiplex signaling system, a transmission circuit, balancing means there- :tor, a plurality of parallel connections between said circuit and balancing means, transmitting and receiving elements for each parallel connection, a transformer balanced to establish conjugate circuits associating one of said elements with the corresponding parallel connection, the other 01"" said elements being so associated with said. pa allel connections that energy from the transmitter will produce substantially no eill'cct upon any of the receivers associated with said multiple connections.

7. In a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means, transmitting and receiving elements for each parallel connection, a transformer balanced to establish conjugate circuits associating one of said elements with the corresponding parallel connection, the other of said elemcnts being connected to points of said parallel connection which are neutral with respect to said first element.

8. In a multiplex signaling system, a transmission circuit, a balancing means therefor, a plurality of receiving channels and a. plurality of transmitting channels, selective means discriminative between different alternating current frequencies, associated with said channels for maintaining frequency separation between said channels, and separate means for associating each of said. receiving channels with said transmission circuit and said balancing means, said transmitting channels being so associated with said transmission circuit and said balancing means that energy from said transmitting channels will produce substantially no effect upon said receiving channels.

9. In a multiplex signaling system, a transmission circuit, a balancing means therefor, a plurality of receiving channels and a plurality of transmitting channels,

filters discriminative between different alternating current frequencies associated with said channels for i'naintaining frequency separation between said channels and separate means for associating each of said receiving channels with said transmission circuit and said balancing means, said transmitting channels being so assoclated with said transmission circuit and said balancing means that energy from said transmitting channels will produce substantially no effect upon said receiving channels.

10.111 a multiplex signaling system a transmission. circuit, balancing means there-i for, a pli'lrality of parallel connections between said circuit and balancing means, a

transmitting apparatus and a receiving apparatus for each parallel circuit associated therewith 1n. con ugate relation with respect to each other, and selective means connected between each transmitting and receiving apparatus and the corresponding parallel connection. I

11. In a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means, a

transmitting and receiving circuit including transmitting and receiving apparatus respectively associated with each parallel connection in conjugate relation with respect to each other, and selective means in said transmitting and receiving circuits. p

12. In a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means,

transmitting and receiving elements for each parallel. connection, a transformer for associating one element of each pair with the corresponding parallel connection, the other of each pair being associated with the corresponding parallel connection in conjugate relation with respect to the first element,and

selective means between the transmitting and receiving elements and their points of association with said parallel connections.

.ln' a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means,

' transmitting and receiving circuitsfor each parallel connection including transmitting and receivingelements respectlvely, a trans- ,rormer for associating one circuit of each pair with the corresponding parallel connection, the other circuit of each pair being conjugately associated with the correspond ing parallel connection, and selective devices j included in said transmitting and receiving ci-cuits between the transmitting and receiving elements and the points of association of the circuits with said parallel connections.

14. In a multiplex signaling system, a transmission circuit, balancing means therefor, a plurality of parallel connections between said circuit and balancing means, a

pairot'circuits, one for transmitting and circuits of at least one pair, and a plurality of receivmg channels associated with the receiving circuit of said pa1r.

In testimony whereof, I have signed my name tothis specification this 26th day of August 1919. 1 o i LLOYD ESPENQCI-IIED. 

